Polypropylene-based terpolymers for films

ABSTRACT

A terpolymer containing propylene, ethylene and an alpha olefins of formula CH2═CHZ wherein Z is an hydrocarbon group having from 2 to 10 carbon atoms wherein: (i) the content of ethylene derived units ranges from 0.5 wt % to 5.0 wt %; (ii) the content of alpha olefin derived units ranges from 1.0 wt % to 5.0 wt %; (iii) the amount (Wt %) of alpha-olefin (C6), the amount (Wt %) of ethylene (C2) and the melting point (Tm) of the terpolymer fulfil the following relation (1) Tm&gt;−(C2+0.8C6)*6+157 (1) (iv) the polydispersity index (PI) ranges from 3 to 8.

This application is the U.S. National Phase of PCT International Application PCT/EP2011/064936, filed Aug. 31, 2011, claiming priority of European Patent Application No. 10175394.5, filed Sep. 6, 2010 and the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application No. 61/403,368, filed Sep. 14, 2010, the contents of which are incorporated herein by reference in their entirety.

The present invention relates to a propylene/ethylene/1-hexene terpolymer particularly fit for the production of biaxially oriented films. Propylene/ethylene/1-hexene terpolymers are already known in the art for the production of pipes or films.

EP 483 523 relates to a compositions of crystalline polymers of propylene of this invention comprise (weight percentage):

-   A) 30-65%, preferably 35-65%, more preferably 45-65%, of a copolymer     of propylene with a C₄-C₈ alpha olefin containing from 98 to 80%,     preferably from 95 to 85%, of propylene; -   B) 35-70%, preferably 35-65%, more preferably 35-55%, of a copolymer     of propylene with ethylene, and optionally from 2 to 10%, preferably     from 3 to 6%, of a C₄-C₈ alpha-olefin, said copolymer containing 2     to 10% ethylene, preferably from 7 to 9% when the C₄-C₈ alpha-olefin     is not present, and 0.5 to 5%, preferably from 1 to 3% ethylene,     when the C₄-C₈ alpha-olefin is present.

The C₄-C₈ alpha-olefin is preferably selected from 1 -butene; 1 -pentene; 1 -hexene; 4-methyl-1-pentene; and 1-octene. Particularly preferred is 1-butene. better results in terms of seal initiation temperature can be obtained by using 1-hexene instead of the preferred monomer 1-butene in particular ranges.

WO2006/002778 relates to a pipe system comprising a terpolymer of propylene/ethylene and alpha olefin wherein the ethylene content is from 0 to 9% by mol, preferably from 1 to 7% by mol and the 1-hexene content ranges from 0.2 to 5% wt. The applicant found that it is possible to select from these ranges a composition having improved properties to be used for films.

U.S. Pat. No. 6,365,682 relates to propylene based terpolymers to be used for films. The ethylene content ranges generally from 1 to 10 wt % and the alpha olefin ranges from 5 to 25wt %. for the preparation of films terpolymers having an ethylene content ranging from 0.9 to 3 wt % and an alpha olefin content ranging from 1 to 15wt % is indicated. Only terpolymer of propylene/ethylene and 1-butene are exemplified. The applicant found that when 1-hexene is used in particular amount the characteristics of the films can be improved.

The applicant has now found that by using a particular polymerization process it is possible to obtain terpolymers having an high melting point, a vey low seal initiation temperature (SIT) at a relatively low content of comonomers. This allows obtaining films with improved features by using low amount of comonomers.

Thus an object of the present inventions is a terpolymer containing propylene, ethylene and an alpha olefins of formula CH2=CHZ wherein Z is an hydrocarbon group having from 2 to 10 carbon atoms such as 1-butene, 1-hexene, 1-octene; preferably the alpha olefin is 1-hexene; wherein

-   (i) the content of ethylene derived units ranges from 0.5 wt % to     5.0 wt %, preferably from 1.0 wt % to 3.0 wt %; more preferably from     1.2 wt % to 2.5 wt % -   (ii) the content of alpha olefin derived units ranges from 1.0 wt %     to 5.0 wt %, preferably from 2.0 wt % to 4.0 wt %; more preferably     from 2.5 wt % to 3.5 wt; -   (iii) the amount (Wt%) of alpha-olefin (C6), the amount (Wt%) of     ethylene (C2) and the melting point (Tm) of the terpolymer fulfil     the following relation (1)     Tm>157−(C2+0.8C6)*6  (1)

Preferably relation (1) is Tm>158−(C2+0.8C6)*6; more preferably Tm>159−(C2+0.8C6)*6; (iv) the polydispersity index (PI) ranges from 2.0 to 7.0, preferably from 3.0 to 6.5, more preferably from 3.5 to 6.0.

The terpolymer of the present invention preferably exhibits a seal initiation temperature (SIT) comprised between 90° C. and 120° C., more preferably between 100° C. and 115° C.; even more preferably between 105° C. and 113° C.

The crystallization temperature preferably ranges from 70° C. to 100° C., preferably from 80° C. to 95° C.; more preferably from 85° C. to 95° C.;

The melt flow rate (MFR) (ISO 1133 230° C., 2.16 kg) of the terpolymer of the present invention ranges from 2 to 20 g/10 min; preferably from 3 to 10 g/10 min.

In order to achieve the MFR of the terpolymer of the present invention it is also possible to visbreak a polymer having a lower MFR. In order to visbreak the polymer known visbreaking agent can be used such as peroxides. With the visbreaking it is possible to fine tune the MFR of the product.

The terpolymers of the present invention have a stereoregularity of isotactic type of the propylenic sequences this is clear by the low value of xylene extractables that is lower than 15%: preferably lower than 12%.

Without to be bound by a theory it is believed that the fact that even at high comonomers content the terpolymers of the present invention show an high melting point is due to the fact that by using the polymerization process described below it is possible to obtain a terpolymer that is multimodalized in composition, i.e. the resulting terpolymer contains various fractions having a low content of comonomers, said fractions being responsible of the high melting point and said terpolymer contains fractions having a quite high comonomer content, said fractions being responsible of the low SIT.

The high melting point allows the terpolymer to be easily processed especially in the production of films. At the same time the low SIT allows the terpolymer to be used easily in various materials such as multilayer films

The terpolymer used in the present invention can be prepared by polymerisation in one or more polymerisation steps. Such polymerisation can be carried out in the presence of Ziegler-Natta catalysts. An essential component of said catalysts is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron-donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminium compound, such as an aluminium alkyl compound.

An external donor is optionally added.

The catalysts generally used in the process of the invention are capable of producing polypropylene with a value of xylene insolubility at ambient temperature greater than 90%, preferably greater than 95%.

Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in U.S. Pat. No. 4,399,054 and European patent 45977. Other examples can be found in U.S. Pat. No. 4,472,524.

The solid catalyst components used in said catalysts comprise, as electron-donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and/or S atoms, and esters of mono- and dicarboxylic acids. Particularly suitable electron-donor compounds are esters of phtalic acid and 1,3-diethers of formula:

wherein R^(I) and R^(II) are the same or different and are C₁-C₁₈ alkyl, C₃-C₁₈ cycloalkyl or C₇-C₁₈ aryl radicals; R^(III) and R^(IV) are the same or different and are C₁-C₄ alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure made up of 5, 6, or 7 carbon atoms, or of 5-n or 6-n′ carbon atoms, and respectively n nitrogen atoms and n′ heteroatoms selected from the group consisting of N, O, S and Si, where n is 1 or 2 and n′ is 1, 2, or 3, said structure containing two or three unsaturations (cyclopolyenic structure), and optionally being condensed with other cyclic structures, or substituted with one or more substituents selected from the group consisting of linear or branched alkyl radicals; cycloalkyl, aryl, aralkyl, alkaryl radicals and halogens, or being condensed with other cyclic structures and substituted with one or more of the above mentioned substituents that can also be bonded to the condensed cyclic structures; one or more of the above mentioned alkyl, cycloalkyl, aryl, aralkyl, or alkaryl radicals and the condensed cyclic structures optionally containing one or more heteroatom(s) as substitutes for carbon or hydrogen atoms, or both. Ethers of this type are described in published European patent applications 361493 and 728769.

Representative examples of said diethers are 2-methyl-2-isopropyl-1,3-dimethoxypropane, 2,2-diisobutyl-1,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-1,3-dimethoxypropane, 2-isopropyl-2-isoamyl-1,3-dimethoxypropane, 9,9-bis (methoxymethyl) fluorene.

Other suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.

The preparation of the above mentioned catalyst component is carried out according to various methods.

For example, a MgCl₂·nROH adduct (in particular in the form of spheroidal particles) wherein n is generally from 1 to 3 and ROH is ethanol, butanol or isobutanol, is reacted with an excess of TiCl₄ containing the electron-donor compound. The reaction temperature is generally from 80 to 120° C. The solid is then isolated and reacted once more with TiCl₄, in the presence or absence of the electron-donor compound, after which it is separated and washed with aliquots of a hydrocarbon until all chlorine ions have disappeared.

In the solid catalyst component the titanium compound, expressed as Ti, is generally present in an amount from 0.5 to 10% by weight. The quantity of electron-donor compound which remains fixed on the solid catalyst component generally is 5 to 20% by moles with respect to the magnesium dihalide.

The titanium compounds, which can be used for the preparation of the solid catalyst component, are the halides and the halogen alcoholates of titanium. Titanium tetrachloride is the preferred compound.

The reactions described above result in the formation of a magnesium halide in active form. Other reactions are known in the literature, which cause the formation of magnesium halide in active form starting from magnesium compounds other than halides, such as magnesium carboxylates.

The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls, such as Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other by way of O or N atoms, or SO₄ or SO₃ groups. The Al-alkyl compound is generally used in such a quantity that the Al/Ti ratio be from 1 to 1000.

The electron-donor compounds that can be used as external donors include aromatic acid esters such as alkyl benzoates, and in particular silicon compounds containing at least one Si—OR bond, where R is a hydrocarbon radical.

Examples of silicon compounds are (tert-butyl)₂Si(OCH₃)₂, (cyclohexyl)(methyl)Si (OCH₃)₂, (cyclopentyl)₂Si(OCH₃)₂ and (phenyl)₂Si(OCH₃)₂ and (1,1,2-trimethylpropyl)Si(OCH₃)₃. 1,3-diethers having the formulae described above can also be used advantageously. If the internal donor is one of these diethers, the external donors can be omitted.

In particular, even if many other combinations of the previously said catalyst components may allow to obtain propylene polymer compositions according to the present invention, the terpolymers are preferably prepared by using catalysts containing a phthalate as internal donor and (cyclopentyl)₂Si(OCH₃)₂ as outside donor, or the said 1,3-diethers as internal donors.

The said propylene-ethylene-hexene-1 polymers are produced with a polymerization process illustrated in EP application 1 012 195.

In detail, the said process comprises feeding the monomers to said polymerisation zones in the presence of catalyst under reaction conditions and collecting the polymer product from the said polymerisation zones. In the said process the growing polymer particles flow upward through one (first) of the said polymerisation zones (riser) under fast fluidisation conditions, leave the said riser and enter another (second) polymerisation zone (downcomer) through which they flow downward in a densified form under the action of gravity, leave the said downcomer and are reintroduced into the riser, thus establishing a circulation of polymer between the riser and the downcomer.

In the downcomer high values of density of the solid are reached, which approach the bulk density of the polymer. A positive gain in pressure can thus be obtained along the direction of flow, so that it become to possible to reintroduce the polymer into the riser without the help of special mechanical means. In this way, a “loop” circulation is set up, which is defined by the balance of pressures between the two polymerisation zones and by the head loss introduced into the system.

Generally, the condition of fast fluidization in the riser is established by feeding a gas mixture comprising the relevant monomers to the said riser. It is preferable that the feeding of the gas mixture is effected below the point of reintroduction of the polymer into the said riser by the use, where appropriate, of gas distributor means. The velocity of transport gas into the riser is higher than the transport velocity under the operating conditions, preferably from 2 to 15 m/s.

Generally, the polymer and the gaseous mixture leaving the riser are conveyed to a solid/gas separation zone. The solid/gas separation can be effected by using conventional separation means. From the separation zone, the polymer enters the downcomer. The gaseous mixture leaving the separation zone is compressed, cooled and transferred, if appropriate with the addition of make-up monomers and/or molecular weight regulators, to the riser. The transfer can be effected by means of a recycle line for the gaseous mixture.

The control of the polymer circulating between the two polymerisation zones can be effected by metering the amount of polymer leaving the downcomer using means suitable for controlling the flow of solids, such as mechanical valves.

The operating parameters, such as the temperature, are those that are usual in olefin polymerisation process, for example between 50 to 120° C.

This first stage process can be carried out under operating pressures of between 0.5 and 10 MPa, preferably between 1.5 to 6 MPa.

Advantageously, one or more inert gases are maintained in the polymerisation zones, in such quantities that the sum of the partial pressure of the inert gases is preferably between 5 and 80% of the total pressure of the gases. The inert gas can be nitrogen or propane, for example. The various catalysts are fed up to the riser at any point of the said riser. However, they can also be fed at any point of the downcomer. The catalyst can be in any physical state, therefore catalysts in either solid or liquid state can be used.

The terpolymer of the present invention, may be blended with additives commonly employed in the art, such as antioxidants, light stabilizers, heat stabilizers, nucleating agents, colorants and fillers.

A further object of the present invention are films, in particularly biaxially oriented films (BOPP) comprising the terpolymer of the present invention.

The following examples are given to illustrate the present invention without limiting purpose.

EXAMPLES

Characterization Methods

-   -   Melting temperature and crystallization temperature: Determined         by differential scanning calorimetry (DSC). weighting 6±1 mg, is         heated to 220±1° C. at a rate of 20° C./min and kept at         220±1° C. for 2 minutes in nitrogen stream and it is thereafter         cooled at a rate of 20° C./min to 40±2° C., thereby kept at this         temperature for 2 min to crystallise the sample. Then, the         sample is again fused at a temperature rise rate of 20° C./min         up to 220° C.±1. The melting scan is recorded, a thermogram is         obtained, and, from this, melting temperatures and         crystallization temperatures are read.     -   Melt Flow Rate: Determined according to the method ISO 1133         (230° C., 2.16 kg).     -   Solubility in xylene: Determined as follows. 2.5 g of polymer         and 250 ml of xylene are introduced in a glass flask equipped         with a refrigerator and a magnetical stirrer. The temperature is         raised in 30 minutes up to the boiling point of the solvent. The         so obtained clear solution is then kept under reflux and         stirring for further 30 minutes. The closed flask is then kept         for 30 minutes in a bath of ice and water and in thermostatic         water bath at 25° C. for 30 minutes as well. The so formed solid         is filtered on quick filtering paper. 100 ml of the filtered         liquid is poured in a previously weighed aluminium container,         which is heated on a heating plate under nitrogen flow, to         remove the solvent by evaporation. The container is then kept on         an oven at 80° C. under vacuum until constant weight is         obtained. The weight percentage of polymer soluble in xylene at         room temperature is then calculated.     -   1-hexene and ethylene content: Determined by ¹³C-NMR         spectroscopy in terpolymers:         NMR analysis. ¹³C NMR spectra are acquired on an AV-600         spectrometer operating at 150.91 MHz in the Fourier transform         mode at 120° C. The peak of the propylene CH was used as         internal reference at 28.83. The ¹³C NMR spectrum is acquired         using the following parameters:

Spectral width (SW) 60 ppm Spectrum centre (O1) 30 ppm Decoupling sequence WALTZ 65_64pl Pulse program ⁽¹⁾ ZGPG Pulse Length (P1) ^((2)\) for 90° Total number of points (TD) 32K Relaxation Delay ⁽²⁾ 15 s Number of transients ⁽³⁾ 1500

The total amount of 1-hexene and ethylene as molar percent is calculated from diad using the following relations: [P]=PP+0.5PH+0.5PE [H]=HH+0.5PH [E]=EE+0.5PE

Assignments of the ¹³C NMR spectrum of propylene/1-hexene/ethylene copolymers have been calculated according to the following table:

Area Chemical Shift Assignments Sequence 1 46.93-46.00 S_(αα) PP 2 44.50-43.82 S_(αα) PH 3 41.34-4.23  S_(αα) HH 4 38.00-37.40 S_(αγ) + S_(αδ) PE 5 35.70-35.0  4B₄ H 6 35.00-34.53 S_(αγ) + S_(αδ) HE 7 33.75 33.20 CH H 8 33.24 T_(δδ) EPE 9 30.92 T_(βδ) PPE 10 30.76 S_(γγ) XEEX 11 30.35 S_(γδ) XEEE 12 29.95 S_(δδ) EEE 13 29.35 3B₄ H 14 28.94-28.38 CH P 15 27.43-27.27 S_(βδ) XEE 16 24.67-24.53 S_(ββ) XEX 17 23.44-23.35 2B₄ H 18 21.80-19.90 CH₃ P 19 14.22 CH₃ H

-   -   Polydispersity Index (PI): Determined at a temperature of         200° C. by using a parallel plates rheometer model RMS-800         marketed by RHEOMETRICS (USA), operating at an oscillation         frequency which increases from 0.1 rad/sec to 100 rad/sec. From         the crossover modulus one can derive the P.I. by way of the         equation:         P.I.=105/Gc         in which Gc is the crossover modulus which is defined as the         value (expressed in Pa) at which G′=G″ wherein G′ is the storage         modulus and G″ is the loss modulus.         Determination of the SIT.

For each test two of the BOPP films are superimposed in alignment, the adjacent layers being layers of the particular test composition. The superimposed specimens are sealed along one of the 2 cm sides with a Brugger Feinmechanik Sealer, model HSG-ETK 745. Sealing time is 5 seconds at a pressure of 0.1 N/mm². The sealing temperature is increased of 2° C. for each seal, starting from about 10° C. less than the melting temperature of the test composition. The sealed samples are left to cool and then their unsealed ends are attached to an Instron machine where they are tested at a traction speed of 50 mm/min.

The SIT. is the minimum sealing temperature at which the seal does not break when a load of at least 2 Newtons is applied in the said test conditions.

Haze on Film

Determined on 50 μm thick films of the test composition. The measurement was carried out on a 50×50 mm portion cut from the central zone of the film. The instrument used for the test was a Gardner photometer with Haze-meter UX-10 equipped with a G.E. 1209 lamp and filter C. The instrument calibration was made by carrying out a measurement in the absence of the sample (0% Haze) and a measurement with intercepted light beam (100% Haze).

Gloss on Film

Determined on the same specimens as for the Haze.

The instrument used for the test was a model 1020 Zehntner photometer for incident measurements. The calibration was made by carrying out a measurement at incidence angle of 60° on black glass having a standard Gloss of 96.2% and a measurement at an incidence angle of 45° on black glass having a standard Gloss of 55.4%.

Examples 1-2 Comparative Examples 3-7

A copolymer is prepared by polymerising propylene, ethylene and hexene-1 in the presence of a catalyst under continuous conditions in a plant comprising a polymerisation apparatus as described in EP 1 012 195.

The catalyst is sent to the polymerisation apparatus that comprises two interconnected cylindrical reactors, riser and downcomer. Fast fluidisation conditions are established in the riser by recycling gas from the gas-solid separator.

In examples 1 and 2 the gas composition in the two reactor legs has been differentiated by using the “barrier” feed according to what described in EP 1 012 195. This stream is propylene fed in the larger upper part of the downcomer. While in comparative examples 3-7 the barrier feed has not been used.

The catalyst employed comprises a catalyst component prepared by analogy with example 5 of EP-A-728 769 but using microspheroidal MgCl₂·1.7C₂H₅OH instead of MgCl₂·2.1C₂H₅OH. Such catalyst component is used with dicyclopentyl dimethoxy silane (DCPMS) as external donor and with triethylaluminium (TEA).

The polymer particles exiting the reactor are subjected to a steam treatment to remove the reactive monomers and volatile substances and then dried. The main operative conditions and characteristics of the produced polymers are indicated in Tables 1-3.

TABLE 1 Examples 1 2 TEA/solid catalyst 4 5 component, g/g TEA/DCPMS, g/g 4 5 C₆/(C₃ + C₆), mol/mol Riser 0.03 0.03 C₆/(C₃ + C₆), mol/mol Downcomer 0.038 0.038 C₂/(C₃ + C₂), mol/mol Riser 0.023 0.022 C₂/(C₃ + C₂), mol/mol Downcomer 0.0035 0.004 C2 ethylene; C3 propylene; C6 1-hexene

TABLE 2 Examples 3* 4* 5* 6* 7* TEA/solid catalyst 5 5 5 5 5 component, g/g TEA/DCPMS, g/g 4 4 4 4 4 C₆/(C₃ + C₆), Riser 0.024 0.026 0.033 0.033 0.031 mol/mol C₂/(C₃ + C₂), Riser 0.007 0.011 0.016 0.015 0.015 mol/mol *comparative C2 ethylene; C3 propylene; C6 1-hexene

The Examples haven been added to additives and peroxides according to tables 3 and 4. Then the polymer mixture is placed in a twin screw extruder Berstorff (L/D=33) and extruded in the following operating conditions:

-   -   temperature of feeding part: 190-210° C.;     -   melt temperature: 235-245° C.;     -   temperature of die part: 210° C.;     -   flow rate: 15 kg/h;     -   rotational speed of the screw: 250 rpm.

TABLE 3 examples 1 2 Irganox 1010 wt % 0.05 0.05 Calcium stearate wt % 0.05 0.05 Irgafos 168 wt % 0.1 0.1 Luperox 101 wt % 0.017 0.013

TABLE 4 examples 3* 4* 5* 6* 7* Irganox 1010 wt % 0.05 0.05 0.05 0.05 0.05 Calcium stearate wt % 0.05 0.05 0.05 0.05 0.05 Irgafos 168 wt % 0.1 0.1 0.1 0.1 0.1 Luperox 101 wt % 0.02 0.032 0.025 0.025 0.025 *Comparative

Biaxially oriented films of the polymers of examples 1-2 and comparative examples 1-5 have been produced the analysis of the films and the characteristics of the polymers are reported on tables 5 and 6

TABLE 5 Example 1 2 MFR g/10 min 6.2 6.6 C6 NMR % 3.3 3.3 C2 NMR % 1.3 1.3 PI 3.9 4.1 XS % 11.3 11.1 IZOD 23° C. 24 h KJ/M2 7 6 Tm ° C. 136.6 137.1 Tc ° C. 90.9 90.2 SIT on BOPP ° C. 110 111 Haze on film % 0.2 0.3 Gloss on film (45′) 96.6 95

TABLE 6 Ex1* Ex2* Ex3* Ex4* Ex5* MFR g/10 min 1.2 0.69 0.93 1.9 0.9 XS % 6.7 6 6.3 2.7 4 Polydispersity index 4.0 4.1 3.9 4.0 4.1 MFR g/10 min 5.2 5.5 6.3 6.6 6.8 C6 NMR wt % 2.7 2.7 2.9 2.5 2.2 C2 NMR wt % 1.7 1.8 1.6 1..0 1.3 IZOD 23° C. 24 h KJ/M2 6.7 7.2 6.7 4.7 5.1 Tm ° C. 132.3 132.3 132.1 137.9 137.1 Tc ° c. 88.1 86.6 86.6 97.1 96.7 SIT on BOPP ° C. 110 110 110 116 116 Haze on film % 0.2 0.2 0.2 0.5 0.2 Gloss on film (45′) N 95.2 96.1 96 95.9 96.3 *comparative

By comparing the features reported on table 5 and the features reported on table 6 it is possible to note that there is an improvement of the melting point together with a very low SIT. In particular example 1 has the same sum of comonomer content of comparative example 3, the sit is the same but the melting point is 136.6 vs 132.3 

The invention claimed is:
 1. A terpolymer comprising: (i) 1.0 to 3.0 wt %, based upon the total weight of the terpolymer, of ethylene derived; (ii) 2.0 to 4.0 wt %, based upon the total weight of the terpolymer, of 1-hexene derived units; and (iii) 93 to 97 wt %, based upon the total weight of the terpolymer, of propylene derived units, wherein the amount of 1-hexene derived units and the amount of ethylene derived units fulfils the following relationship (1): Tm>159−(C2+0.8C6)*6  (1) wherein C6 is the amount of 1-hexene derived units in wt %, C2 is the amount of ethylene derived units in wt %, and Tm is the melting point of the terpolymer, wherein the terpolymer has a polydispersity index (PI) ranging from 2.0 to 7.0, and a melt flow rate from 2 to 20 g/10 min, as measured at 230 ° C. and 2.16 kg.
 2. The terpolymer according claim 1, wherein the polydispersity index ranges from 3.5 to 6.0.
 3. The terpolymer according to claim 1, wherein the terpolymer has a crystallization temperature ranging from 70° C. to 100° C.
 4. A film comprising: a terpolymer, wherein the terpolymer comprises (i) 1.0 to 3.0 wt %, based upon the total weight of the terpolymer, of ethylene derived; (ii) 2.0 to 4.0 wt %, based upon the total weight of the terpolymer, of 1-hexene derived units; and (iii) 93 to 97 wt %, based upon the total weight of the terpolymer, of propylene derived units, wherein the amount of 1-hexene derived units and the amount of ethylene derived units fulfils the following relationship (1): Tm>159−(C2+0.8C6)*6  (1) wherein C6 is the amount of 1-hexene derived units in wt %, C2 is the amount of ethylene derived units in wt %, and Tm is the melting point of the terpolymer, wherein the terpolymer has a polydispersity index (PI) ranges from 2.0 to 7.0, and a melt flow rate from 2 to 20 g/10 min, as measured at 230 ° C. and 2.16 kg.
 5. The film of claim 4, wherein the film is a biaxially oriented film.
 6. The film of claim 4, wherein the film has a seal initiation temperature (SIT) between 90 and 120° C. 